This invention relates to centrifuge rotors and, more particularly, to the swinging bucket type of centrifuge rotor.
Swinging centrifuges typically include a rotor having a plurality of peripheral cavities therein. Each cavity houses a swinging member, usually referred to as a bucket, which holds the material to be centrifuged. The buckets are pivotally mounted in each cavity, such that they normally hand with a vertical orientation. As the rotor increases speed, the buckets, because of centrifugal force, swing outwardly and desirably assume a horizontal position. The pivotal mounting is provided with some means of flexure by which the buckets, under the influence of extreme centrifugal force at their high speed of rotation, are permitted to move radially outward until they are supported by or seated within the rotor cavity itself such that they are restrained from further outward movement. The reverse sequence occurs as the rotor is slowed down, i.e., the buckets are retracted radially inward such that they unseat from the rotor cavity and are allowed to swing back down to a vertical orientation.
Among the early designs of these type of rotors, flexure was provided by elongated pins which extend through a section of the rotor. Unfortunately these pins required a relatively large amount of rotor space and severely limited the number of cavities and, hence, the number of buckets that could be positioned within one rotor.
An improvement over this design which permitted the use of more swinging buckets in a given rotor was provided by Galasso et al. in U.S. Pat. No. 3,393,864, issued July 23, 1968. Galasso et al. taught that each of the buckets is supported by an independent bucket hanger assembly disposed within a cavity in the rotor. Each hanger assembly is spring biased in a radially inward sense toward the axis of rotation of the rotor and includes a separate pin member carried by the assembly from which a bucket can be suspended. While the Galasso et al. apparatus was a vast improvement over the elongated pin montings, it unfortunately has many disadvantages. Among these disadvantages, the hanger mounting screws can and do become loosened with use and vibration and the required precise positioning of that bucket is lost. The bucket can then rotate which may cause it to drop off or not seat properly. Either results in an unbalanced rotor and can cause possible rotor spin-off at high speed. The resulting damage can be very expensive.
Another swinging bucket rotor is described by Chulay, in U.S. Pat. No. 3,752,390, issued Aug. 14, 1975. In Chulay the rotor cavities each have a vertically positioned torsion bar extending downwardly through the rotor into the bucket cavity. A disadvantage of the Chulay assembly, as well as the Galasso et al. assembly, is that the bucket, which must be precisely mounted, can easily be mounted improperly, e.g., backwards, by the careless user. This can result in rotor unbalance. Further, the buckets can be improperly mounted such that they are not securely positioned by the hook support provided. In this case, the buckets may fly off as soon as the rotor begins operation.
The disadvantages of both Chulay and Galasso et al. are overcome to a large extent by a centrifuge rotor developed by John Williams and Mark Hayden. According to Williams et al., the hanger is slidably positioned in a receptacle which prevents its rotation about its path of movement. The hanger hook provided by Williams et al. supports a cross-pin located in the bucket cap. The hook is formed with a downwardly sloping entrance opening so that the bucket can only be mounted in a proper manner. Further, the cross-pin is designed to permit only a proper mounting of the bucket.
One disadvantage of Williams et al. as well as Galasso et al. and Chulay is that the range of different weight buckets that can be used with a single rotor is somewhat limited. If buckets having a weight outside this permitted range are to be used, the hanger assembly must be changed, which is somewhat time consuming and cannot, of corse, be accomplished until the rotor is not in use.
Accordingly, it is an object of this invention to obviate many of the disadvantages of the prior art swinging bucket type centrifuges.
An additional object of this invention is to provide an improved centrifuge rotor which is capable of accommodating more than one weight sets of swinging members.
A further object of this invention is to provide an improved centrifuge rotor in which the swinging member is provided with a spring loaded cap.